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Here, using liquid crystals as template, an EISA (evaporation-induced self-assembly) method has been used to synthesize amorphous mesostructured alumina. The effect of the synthesis parameters such as the presence of a chelating agent, the amounts of both porogen agent and alumina precursor on the materials properties have been investigated in details. Under the optimum conditions, after Soxhlet extraction, the obtained Al 2 O 3 presents an HMS (Hexagonal Molecular Sieves) structure and a high specific surface area (≈400 m2/g) with a mesopore size distribution centered around 8.3 nm. Investigation of the thermal stability shows that the crystallization into γ-Al 2 O 3 of the amorphous alumina walls delimiting mesopores begins after heating at 800 °C. We have also demonstrated that half of the carbon present in the as-synthesized material can be removed by washing with water or ethanol at room temperature instead of Soxhlet extraction. On the basis of SAXS, XRD and N 2 adsorption-desorption analyses, we have shown that when treated into boiling water or exposed to water vapor the alteration of the mesostructure occurs quickly. Its collapse has been attributed to the crystallization of the amorphous alumina walls into aluminum hydroxides, mainly boehmite, upon the hydration of the alumina. Dual mesoporous alumina have been also obtained from micelles through a cooperative templating mechanism at low P123 amount and in the presence of citric acid. In that case both mesopores networks adopt a wormhole-like mesostructure. [Display omitted] • Mesostructure preserved until 900 °C. • Amorphous mesostructured Al 2 O 3 thermally stable up to 800 °C. • Porogen agent partially removed by water or ethanol at room temperature. • Framework collapses due to aluminum hydroxides crystallization in presence of water. • Dual mesoporous alumina prepared at low amount of porogen agent in presence of citrate. [ABSTRACT FROM AUTHOR]

The effect of the introduction of heteroelement (Si, P, Al, Ge, Ga and Zr) by direct synthesis on the thermal stability of mesostructured titania prepared by the soft templating pathway has been investigated. All materials have been surfactant-extracted with EtOH and calcined at different temperatures up to 900 °C. Ti4+ can be partially substituted by most of the investigated heteroelements but they mainly form an oxide amorphous phase surrounding the titania anatase particles. Results obtained by SAXS, X-Ray diffraction, Raman spectroscopy and manometry nitrogen adsorption-desorption show that the crystallization of the amorphous titania into nanosized anatase particles and the transition from anatase to rutile occur at higher temperature with the addition of the heteroelement. Even if the lattice distortion introduced by the partial Ti4+ substitution can participate to this phenomenon, it is mainly due the «glass » effect induced by the presence of the heteroelement in the TiO 2 amorphous phase, which limits the growth of the nanosized anatase crystallites. However, when the crystallites reach a limit size, the collapse of the mesostructure occurs. With increasing the calcination temperature, the anatase titania particles become bigger and bigger, the transition from anatase to rutile takes place and the heteroelement can crystallize or be integrated in a crystalline phase. Among the considered heteroelements and by comparison with the bare mesostructured TiO 2 , the most beneficial effect is obtained in the presence of Si4+ and PO 4 3− for which the mesostructure collapse at higher temperature by about two hundred Celsius degrees. Al3+ and Ge4+ enhance the thermal stability by about a hundred Celsius degrees and Ga3+ or Zr4+ have no significant effect on the temperature at which the mesostructure collapses. Image 1 • Thermal stability of mesostructured TiO 2 enhanced by the addition of heteroelements. • Heteroelements form amorphous phase which embedded the anatase particles and inhibit their growth. • Limit size reached by anatase particles involves the collapse of the mesostructure. • Delay of the anatase to rutile transformation in the presence of heteroelements. • Partial substitution of titanium by the heteroelement. [ABSTRACT FROM AUTHOR]